This invention relates to capacitive liquid sensing and analysis systems.
When two miscible fluids are mixed it is often desirable to determine the relative amount of each fluid which is present. In the case of coolant, for example, where alcohol or ethylene glycol is mixed with water, the freezing point of the liquid depends on the relative amounts of the two liquids. The relative amounts of the two liquids may be determined by using a density measuring device or hydrometer, for example, when coolants are involved so that the freezing point of the liquids may be ascertained.
However, known techniques, such as the use of a hydrometer, are not always convenient or readily compatible with electrical monitoring systems.
The disclosure of U.S. Pat. No. 5,824,389 is also noted. However, this patent does not relate to miscible liquids, but to the deterioration of a single liquid, or to the presence of an immiscible contaminant, such as water present in oil.
It is therefore an object of the invention to provide a simple electrical sensor for determining the relative concentration of miscible liquids, with such sensor being compatible with electronic systems such as feedback and control systems.
In accordance with one illustrative system, the relative concentration of two miscible liquids in a tank or other container may be determined by a capacitive sensor. With the dielectric constant of one fluid being different from the dielectric constant of the other fluid, the sensor and its associated circuitry have offset and gain control arrangements so that the electrical signal output of the sensor has a range extending linearly from a low output value when the dielectric constant of the mixture is equal to that of one of the liquids, up to a maximum when the dielectric constant of the liquid approaches that of the other of the liquids.
A feedback circuit may be provided to change the operation of the system in accordance with the relative concentrations of the liquids. In one illustrative example, the two liquids may be mixed in a tank, and electromagnetically actuated valves from two sources of liquids may be actuated selectively to keep the concentration in the tank at the desired proportions.
Feedback circuits controlling other operating parameters may also be used. For example, in the case of antifreeze, a heater may be employed to prevent temperatures from dropping below the freezing temperature of the coolant.
Other objects, features and advantages of the invention will become apparent from a consideration of the following detailed description and from the accompanying drawings.